Sergei, Bo-na's childhood friend and a mercenary from Russia, reappears, and the truth of The Gosiwon Case in Haegong-dong from four years ago begins to surface. Bo-na investigates Sergei's return to Korea. Meanwhile, Dong-jin learns that Jang Eun-hak, the culprit who murdered his parents, has been paroled.

Dong-jin recalls that Tae-sung's assailant and Kingfisher were in the same building in the past. He immediately proceeds with an interview with the assailant, during which he obtains a clue that Kingfisher might be a woman. Meanwhile, Bo-na catches her mother-in-law's Voice Phishing culprit and receives recognition from her mother-in-law. Although the family becomes harmonious, Tae-sung's anxiety steadily intensifies.